Micro-structured fiber Bragg gratings: optimization of the fabrication process.

This work has been devoted to present and demonstrate a novel approach for the fabrication of micro-structured fiber Bragg gratings (MSFBGs) with enhanced control of the geometric features and thus of the spectral properties of the final device. The investigated structure relies on the localized stripping of the cladding layer in a well defined region in the middle of the grating structure leading to the formation of a defect state in the spectral response. In order to fully explore the versatility of MSFBGs for sensing and communications applications, a technological assessment of the fabrication process aimed to provide high control of the geometrical features is required. To this aim, here, we demonstrate that the optimization of this device is possible by adopting a fabrication process based on polymeric coatings patterned by high resolution UV laser micromachining tools. The function of the polymeric coating is to act as mask for the HF based chemical etching process responsible for the cladding stripping. Whereas, UV laser micromachining provides a valuable method to accurately pattern the polymeric coating and thus obtain a selective stripping along the grating structure. Here, we experimentally demonstrate the potentiality of the proposed approach to realize reliable and cost efficient MSFBGs enabling the prototyping of advanced photonics devices based on this technology.

Mode transition in high refractive index coated long period gratings.

In this work, the numerical and experimental investigation of the cladding modes re-organization in high refractive index (HRI) coated Long Period Gratings (LPGs) is reported. Moreover, the effects of the cladding modes re-organization on the sensitivity to the surrounding medium refractive index (SRI) have been outlined. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness) and on the SRI. In particular, if layer parameters are properly chosen, the transition of the lowest order cladding mode into an overlay mode occurs. As a consequence, a cladding modes re-organization can be observed leading to relevant improvements in the SRI sensitivity in terms of wavelength shift and amplitude variations of the LPGs attenuation bands.

[The effects of eradication therapy in patients with chronic atrophic gastritis and seropositivity for anti-HP antibodies and histological negativity for Helicobacter pylori]. / Effetti della terapia eradicante in pazienti affetti da gastrite cronica atrofica con sieropositività per gli anticorpi anti-HP e negatività istologica per l'Helicobacter pylori.

PURPOSE: The present study was undertaken to analyze both whether the elevated Helicobacter pylori levels in patients with atrophic gastritis without histologic evidence of Helicobacter pylori would be a sign of an ongoing infection and the effects of eradication on gastric atrophy. PATIENTS AND METHODS: Twenty patients (10 M e 10 F; mean age 57.25 SD 12.19) with atrophic gastritis and elevated Helicobacter pylori titers without histological evidence for Helicobacter-like organisms were included in the study. Ten patients were randomized into eradication group (Group 1) (amoxicillin at 500 mg twice a day for 14 days, metronidazole at 500 mg twice a day for 10 days and omeprazole at 20 mg twice a day for 20 days) and 10 patients were randomized into the control group (Group 2). For all subjects, serum samples and duplicate biopsy specimens (obtained endoscopically) were collected prior the study period and approximately 6 months after the therapy or the follow-up for serum samples and 8 weeks for biopsy specimens. RESULTS: In the Group 1, the Helicobacter pylori antibody titers dropped significantly in 73.39% of the patients (p < 0.0001), while in the Group 2, the antibody titers declined only in a patient who received antibiotics during the study period (p < 0.00006). In both groups, no significant improvement of atrophic gastritis was observed. CONCLUSIONS: In conclusion, in patients with atrophic gastritis, the only histological evaluation of Helicobacter-like organisms colonization in gastric biopsy specimens, appeared in our study to underestimate the true prevalence of current HP infection and the importance of the bacterium in the pathogenesis and progression of such disease. Since HP infection is often associated with an increase of proliferative index, the eradication of HP could induce a mucosal protective effect against the other carcinogen factors, although it is extremely unlikely that it can promote the regeneration of a normal gastric mucosa.